From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 16110 invoked by alias); 29 Nov 2011 11:26:35 -0000 Received: (qmail 16098 invoked by uid 22791); 29 Nov 2011 11:26:34 -0000 X-SWARE-Spam-Status: No, hits=-2.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 29 Nov 2011 11:26:21 +0000 From: "marc.glisse at normalesup dot org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/51336] [C++11] is_abstract and sfinae Date: Tue, 29 Nov 2011 12:02:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: marc.glisse at normalesup dot org X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Status Resolution Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2011-11/txt/msg02768.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51336 Marc Glisse changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |UNCONFIRMED Resolution|INVALID | --- Comment #8 from Marc Glisse 2011-11-29 11:26:19 UTC --- (In reply to comment #7) > IMO a warning could be very useful here (at least in circumstances where the > constructor is never reachable). Ok, reopening then. Not sure how easy it is to test for reachability in general, but there are certainly easy cases where it is doable. > While it seems that the current defect in regard to concept-constrained member > functions mentioned in c++std-core-20783 is a defect, so that > > template > class A { > requires SomeConcept > A(const A&) {} > }; > > is *intended* to work, That would be great. I assume that when T doesn't satisfy SomeConcept, the compiler can still generate a default copy constructor (we can always have a deleted copy constructor with requires !SomeConcept if we don't want it). > I currently see no such chance for sfinae-constrained > special-member functions - unless the new temploid nomenclature shows that in > > template > struct A { > template std::enable_if::value>::type > > > A(A const&){} > }; > > A::A(A const&) is considered as a temploid as well. I stay tuned to see how > "temploids" will be defined... Looks interesting, although since we're talking about a future standard (at least I assume that's what you are talking about? Or are temploids coming up as a bugfix for C++11?), I'd rather write (see around c++std-ext-11764): static if(std::is_same()) A(A const&){ /* special code */ } > Your suggested addition of a copy-constructor to non-const is surely useful in > some cases, but I think the emulation is imperfect. Just consider that you try > to copy from a source that is not const. I completely agree, I was just trying to see if there was any possibility for the templated "copy" constructor to have any effect (not even necessarily a useful one). If there had been none, a warning was definitely warranted.